Stringent complete response (sCR) criteria may not predict clinical outcomes for patients with multiple myeloma (MM) compared with complete response (CR) criteria, according to study findings presented at the 2018 American Society of Hematology (ASH) Annual Meeting and Exposition in San Diego, California.

The current sCR criteria include all CR parameters plus the requirement of a normal free-light chain ratio (sFLCr) in the absence of clonal plasma cells in bone marrow by immunohistochemistry. In this phase 3 study, researchers aimed to confirm preliminary data from a previous study that demonstrated abnormal sFLCr did not influence the outcome of patients with MM.

Data were collected from 459 patients with newly diagnosed MM who had previously participated in the GEM05MENOS65 study and had been enrolled in a subsequent maintenance trial. The researchers defined normal sFLCr as 0.26 to 1.65 and abnormal sFLCr as below 0.26 if the patient was λ or above 1.65 if the patient was κ.

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Patients were monitored for minimal residual disease (MRD) and assessed for morphological enumeration of plasma cells using next generation flow cytometry, with a median detection limit of 3 x 10-6. Patients were classified as achieving sCR if they met CR criteria and had a normal sFLCr in the absence of clonal plasma cells at a threshold of sensitivity of 10-4.

After a median follow-up of 40 months, 239 of 392 evaluable patients achieved CR or better. Complete information about sFLCr and MRD was available for 208 patients in CR, of whom 153 achieved sCR. Of the 55 patients who did not achieve sCR, 44 patients had abnormal sFLCr, 6 patients had MRD, and 5 patients experienced both.

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